Technologies related to a road-to-vehicle communication and an inter-vehicle communication have been developed so far. By means of the road-to-vehicle communication, information related to a road is sent from an infrastructure equipment, provided on the road, to a vehicle, and by means of the inter-vehicle communication, information is directly sent from an own vehicle to the other vehicle by use of a communication device provided at the own vehicle. Those technologies are used for improving safe driving.
Specifically, those technologies are used for preventing vehicles from colliding at intersections where low visibility is prevalent and the like. For example, in a case where a vehicle is approaching the intersection with low visibility, information indicating that the own vehicle is approaching the intersection is sent by means of an antenna attached to a front portion of the own vehicle to another vehicle approaching the own vehicle, so that the other vehicle may recognize in advance that the own vehicle is approaching the intersection. This communication may be appropriately executed by use of an antenna having a directional characteristic (hereinafter referred to as a directional antenna). On the other hand, in a case of the road-to-vehicle communication, because the own vehicle basically communicates with a base station provided along a road ahead of the own vehicle, an antenna not having a directional characteristic (hereinafter referred to as a non-directional antenna) may be used for appropriate communication. Disclosed in JP2005-174237A and JP2008-153813A are communication devices being equipped with a directional antenna and a non-directional antenna.
An inter-vehicle communication device of JP2005-174237A mounted to an own vehicle wireless-communicates with a communication device mounted to another vehicle. The inter-vehicle communication device is configured by antennas, a directional characteristic changing means and the like, and on the basis of information related to a road condition, for example information of an existence of an intersection ahead of the own vehicle, the antenna is switched to be used as a transmitter or a receiver, at the same time, a directional characteristic of a radio wave to be sent or to be received is changed by use of the antenna.
A small wireless communication device disclosed in JP2008-153813A is configured by an excitation element of an integrated antenna and passive elements positioned in the vicinity of the excitation element of the integrated antenna. The small wireless communication device changes a directional characteristic of an antenna by turning on/off a connection between the excitation element and the passive element via a semiconductor element.
According to the communication device used for the vehicle-to-vehicle communication disclosed in JP2005-174237A, the antenna itself is physically rotated in order to change a directional characteristic of a radio wave to be sent/received, the device needs to be formed with a actuating portion for actuating the antenna and a controlling portion by which the actuation of the actuating portion is controlled. Accordingly, a circuit structure and a mechanism of the device are more complicated, thereby increasing a cost thereof.
Further, according to the small wireless communication device disclosed in JP2008-153813A, in order to change a directional characteristics of a radio wave to be sent/received, because a directional characteristic of the integrated antenna of the device is directly changed by turning on/off the connection between the excitation element and the passive element via the semiconductor element, the small wireless communication device needs to be formed with a plurality of passive elements and a control circuit by which the connection between the excitation element and the passive elements are electrically turned on/off. Accordingly, a structure of the control circuit is more complicated. Furthermore, because an available antenna does not have the abovementioned configuration, the antenna disclosed in JP2008-153813A needs to be newly developed, thereby increasing a cost thereof.
A need thus exists to provide a vehicle-mounted communication device, which is not susceptible to the drawback mentioned above.